F-35A testing and evaluation at Mountain Home Air Force Base
As the military considers basing F-35s in Boise, a team of Air Force evaluators has wrapped up an inspection of the facilities at Gowen Field, which shares the Boise Airport’s runways.
The Air Force is expected to announce a decision this fall on whether it has chosen Gowen for a squadron of F-35s. If it picks Gowen, the Air Force will conduct an environmental impact study on how the F-35s — particularly their noise — would affect Boise.
Until then, the science on how F-35s at Gowen would affect Boise residents is incomplete.
Q: Just how loud is the F-35?
There’s a lot of conflicting data. Measurements taken last year in Amsterdam found similar noise levels between the F-35 and F-16, another fighter jet, though people who lived near that airfield thought the F-35 was “less noisy than the high-pitch whine produced by the F-16,” according to a report by Aviation Week, a publication that specializes in military coverage.
One study from 2014 found the F-35’s ground noise was within one decibel of the noise from other Air Force fighters, such as the F-15, F-16 and F-22. But those comparisons were the result of varied methods, including technical reports dating back to 2002, as well as noise measurements taken in 2013 at Edwards Air Force Base.
Monty Mericle said he doesn’t trust on-site noise measurements for comparing aircraft types because they rely on too many variables — weather, equipment, aircraft payload, etc. — and are too easy to manipulate. An electrical engineer by trade, Mericle is a prominent opponent of Gowen’s F-35 push. He lives in the Hillcrest Neighborhood just north of the airport’s runways, where the Guard’s planes take off and land.
Mericle said computer modeling is a more reliable noise-measurement method as long as it uses “non-slanted inputs (that) produce consistent, accurate results.” He also believes the people who develop computer models should calibrate their findings with real-life measurements. According to the Federal Aviation Administration, though, “noise monitoring is not required and should not be used to calibrate the noise model.”
Mericle said the the 2014 study’s reliance on a variety of different methods further reduces its credibility.
Efforts to contact aircraft noise experts, including private consultants, the military and the FAA, to verify Mericle’s suspicions were unsuccessful.
The FAA requires computer models for maps showing the impact of airport noise. The Air Force also relies on models for environmental impact statements, which are thorough documents that examine the noise impacts of military aircraft.
For example, the Air Force conducted a 1,068-page environmental impact statement in 2012 as it considered basing an F-35 pilot training center at Gowen or other military bases around the West.
Here are maximum sound levels, in decibels, produced by various warplanes during a 345-mph takeoff, as heard from 500 feet away, according to the Air Force’s 2012 statement:
Q: How much difference can a few decibels make?
It’s a tricky calculation. On one hand, a difference of three decibels or less is “not readily detectable outside of a laboratory environment,” according to a noise study the Boise Airport commissioned and the FAA approved in 2015.
The same study agreed with a broad swath of noise experts that, to most people, adding six to 10 decibels makes an airplane twice as loud.
This is the problem with conflicting data. According to the Air Force’s 2012 environmental impact statement, the F-35 is more than twice as loud as the F-15 and more than four times as loud as the A-10s stationed in Boise now, even by the most conservative calculations. But according to some on-site measurements, there’s almost no difference between an F-35, an F-15 and an F-16.
Q: How does military aircraft noise affect Boise?
Besides their own enjoyment of life, neighbors of the airport fear a wing of F-35s would reduce their homes’ values. They cite reports and analyses that found homes near airports were significantly less valuable than their peers in other neighborhoods, though it’s difficult to tell how much difference an increase in airport noise makes.
No one has has produced an official study on an F-35 mission like the one being considered for Boise now. The Air Force would conduct such an analysis if it picks Gowen Field for an F-35 squadron. If that examination turned up something untenable, such as an unacceptable noise impact, the Air Force would deny Gowen the F-35 mission, experts say. The analysis also would suggest noise-mitigation steps.
The airport’s 2015 study predicted that swapping F-15s for the A-10s would put 419 homes and 1,050 residents inside an area that would be exposed to a 65-decibel average noise level, which the FAA considers the threshold for compatibility with residential use. (This noise level calculation gives more weight to nighttime sounds because they’re more disruptive.)
The same study found 89 homes with an estimated population of 260 inside the 65-decibel area with A-10s stationed at Gowen. A 1994 study found that a squadron of F-4s, which preceded the A-10s at Gowen, put 1,003 homes inside the 65-decibel threshold.
During the preparation of its 2015 study, the airport produced a preliminary map showing 270 homes inside the 65-decibel line if F-35s were here. But that map isn’t part of the official record because the purpose of the study was to project the amount of noise the airport would produce in 2020, and F-35s wouldn’t arrive at Gowen until well after that.
The Air Force’s 2012 environmental impact statement produced a noise map predicting that an F-35 training mission would expose 3,104 residents to the 65-decibel noise level. But that map was based on a pilot training mission, not the operations mission the Air Force is considering now. It assumed Gowen would have 24 F-35s making more takeoffs and landings per year than the operations mission, on top of the roughly 2,500 yearly trips by the Guard’s existing wing of A-10s. That increased the Air Force’s average noise projections.
Q: How many flights would this mission’s F-35s make?
The proposed new F-35 mission would replace Gowen’s 18 active A-10s with a similar number of planes, making around 2,400 yearly trips.
“During the last five years, the Idaho Air National Guard has flown fewer than 10 sorties per flying day with approximately 20 flying days per month,” Idaho National Guard spokesman Chris Borders said in an email.
So the F-35 mission being considered now would produce less noise, on average, than the Air Force’s 2012 environmental impact statement projects, though no one knows by how much. That is why the Guard considers the Air Force’s 2012 study irrelevant to today’s discussion.
Q: How often would the planes take off and land?
The Guard expects the frequency of training flights to remain roughly the same if the F-35 or some other plane is based here.
“On average, the majority of the training currently takes place Monday through Friday during daylight hours, with takeoffs usually around mid-morning and again in early afternoon,” Borders said.
Usually, between two and four aircraft take off within a few seconds of each other, though as many as six aircraft could take off occasionally, he said.
Q: Why doesn’t the Guard bring in F-35s for a trial run and settle the issue?
Many people have asked this question, since it seems sensible to try out the F-35 in Boise before making a basing decision.
In fact, the Idaho Air National Guard has an open request to the Air Force to bring an F-35 to Boise this fall for the Gowen Thunder Air Show, Borders said. But that request hasn’t been fulfilled yet, and availability of the aircraft and qualified pilots may keep it from happening.
Q: Is there any way to reduce the noise?
The airport is considering measures aimed at reducing the impact of noise on the surrounding civilian population. Its proposals include buying houses from willing owners inside or next to the 65-decibel line or outfitting some of those homes with sound insulation and sound-resistant windows, spokesman Sean Briggs said in an email.
The airport also is seeking an FAA grant to cover the cost of installing a sound-monitoring system near its runways.
The Guard is considering measures that would reduce the noise its jets produce, not just the impact on neighbors, Borders said. Those include taking off and landing in the direction that’s least disruptive to neighbors; limiting the power aircraft use when they are near residential areas; observing quiet hours between 7 p.m. and 7 a.m.; and restrictions on afterburner use.
Another much-discussed option is the expansion of a third runway about a mile south of the airport’s two main runways, which Gowen’s planes also use. This runway already exists but is too small for the Guard’s purposes.
A new military-scale third airstrip likely would take many years to complete. Airport officials say the FAA is unlikely to shell out the money needed to expand it before a team of F-35s lands here.
If it were built, the runway’s location would reduce noise exposure to homes near the other two runways and would be used primarily for military operations, at least initially.
Q: Is the airport forcing people to sell their homes?
No. Since 2000, the airport has bought about 25 nearby homes with FAA grant money, but all of those transactions were voluntary, Briggs said.
“The Boise Airport has never forced someone to sell their property,” he said.
City leaders say the airport has no plans to buy people’s homes without their consent.
In addition, over the past 40 years, the airport has acquired avigation easements for 6,700 acres of homes and other properties surrounding it, including 83 of 89 homes inside the current 65-decibel perimeter, Briggs said. In signing these easements, property owners grant the airport and Guard the right to fly at any altitude over their property.
Q: Does Boise’s noise ordinance apply to Gowen Field?
No. The noise ordinance applies only to sound from a “loud amplification device” such as a stereo, but not to airplanes.
Q: What can I do if the airport is too noisy?
Call the airport’s front desk at 208-383-3110 if you hear excessive airplane noise. Try to relay, as precisely as possible, the time you heard the noise. That helps the airport figure out which flight — military or commercial— caused the noise.
The airport fields about two to three of these calls per month, most commonly in the early spring and when the weather is cloudy, Briggs said.
If the Air Force picks Gowen for the F-35 mission, the public will have a chance to comment when the military conducts its environmental impact study.
The science behind noise maps
Noise exposure maps look simple enough, but they take into account a dizzying list of factors, including aircraft types, flight frequency, direction of takeoff and landing, topography and operating time.
The lines on the maps, identifying noise threshold contours, are somewhat misleading. The line people focus on most is called the 65-decibel contour. On its own, 65 decibels is no big deal — somewhere between the loudness of a conversation in a restaurant and a vacuum cleaner. But the FAA considers the 65-decibel contour the threshold for compatibility with residential use.
How can that be? It’s because the 65-decibel boundary identifies average sound — essentially the anticipated level of sound averaged over the course of a given day. Of course, noise doesn’t occur consistently. It rises and falls, especially when airplanes are involved. Airport noise exposure maps flatten those peaks and valleys into a single number.
If that’s not complicated enough, try this: Those noise maps give extra weight to nighttime sounds because they’re more disruptive, especially to neighborhoods. Besides, a house located just outside the 65-decibel line isn’t completely free of noise. People living in that house might experience virtually the same level of noise as a next-door neighbor whose house is just inside the 65-decibel line. The sound gradually recedes as you move farther from the source, which is the runway in this case.